Apparatus and method of operating a forced flow once-through vapor generating power plant



April 5, 1966 v. z. CARACRISTI APPARATUS AND METHOD OF OPERATING A FORCED FLOW ONCE-THROUGH VAPOR GENERATING POWER PLANT Filed Nov. 20, 1962 2 Sheets-Sheet l FINISHIZNG SUPERHEATER I I l l l I PRIMARY SUPERHEATER AUXILIARY VAPOR SOURCE DEAERATOR I l I I 1 l l 1 l I l VAPOR E G E NE RATING SECTION [1 mill 1 24 hillllllmlllll INVENTOR. VIRGINIUS Z. CARACRISTI BY @441? 25/ AGENT April 5, 1966 v. z. cARAcRlsTl APPARATUS AND METHOD OF OPERATING A FORCED FLOW ONCE-THROUGH VAPOR GENERATING POWER PLANT Filed Nov. 20, 1962 2 Sheets-Sheet 2 DEAERATOR d 5 E 6 YR v mm 8 S $2 3 W a (AP m. E 2 w 0 m M 4 2 E E H U R E S P E w m H G m R N E M m I l I l l I l I l l I l I '0 m m m N T C H m 7 n 2 5 2 w 5 2 .1 l l l I I l I l I l l l l l I I l I l l l l l l I IIL FIG. 2

INVENTOR: VIRGINIUS Z. CARACRISTI ig/4;

AGENT Patented Apr. 5, 19%? 3,243,961 APPARATUS AND METHOD OF OPERATING A FORCED FLOW ONCE-THROUGH VAPOR GEN- ERATING POWER PLANT Virginians Z. Caracristi, West Hartford, Conn, assignor to Combustion Engineering, Inc, Windsor, Conn, a corporation of Delaware Filed Nov. 29, 1962, Ser. No. 238,886 9 Claims. (Cl. 60-105) The invention relates in general to a forced flow modified once-through vapor generating power plant and more particularly, to an apparatus and method for starting up a forced flow once-through type steam generator and turbine associated therewith.

In starting up a forced flow once-through steam or vapor generator it is very important for economical reasons to reduce as much as possible the time required for bringing the unit on the line and the amount of heated vapor or steam required for safe starting, which vapor or steam is not directly used to generate electric power.

For start up operation, a vapor power plant can be divided into essentially two major portions. The liquid heating and vapor generating portion, and the vapor heating and turbine portion. Both the turbine as well as the vapor generator require several hours for heating to bring these portions up to the proper operating temperature without exceeding permissible thermal stresses. Conventionally the vapor generator is first started up and the temperature and pressure of the working fluid raised to a desired degree and value before vapor is admitted to the turbine for rolling and heat conditioning of the turbine. Both of these procedures require several hours for their safe execution. Although they may over-lap chronologically to some extent, the time required to bring a unit on the line is undesirably prolonged by the sequential nature of the start up procedure. Furthermore, in modern high capacity high pressure vapor generators, large quantities of heated working fluid are utilized in the starting up operation of these power plant. The heat contained in the vast quantities of working fluid thus passing through the heating surfaces is largely lost in the condenser. It is, accordingly, of prime economic importance in starting up high capacity high pressure forced once-through flow vapor generators and turbines, not only to reduce the time required for start-up, but also to reduce the heat lost in the working fluid that is being discharged to drain or to the hot well during starting up operation.

Accordingly, it is a primary object of the invention to reduce by a significant degree the time necessary for starting up a forced flow once-through vapor generator and turbine power plant.

An additional important object of the invention is to conserve heat during the start-up operation by reducing the quantity of heat lost through the condenser system.

Other objects and advantages will become apparent as the description of illustrative embodiments of the invention proceeds. The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. These claims as well as the following description of the invention will best be understood when read in conjunction with the accompanying drawing in which:

FIG. 1 is a representation of a vapor power plant system in the form of a flow diagram incorporating the features or the present invention when employed in a vapor generator having a primary and finishing superheater.

FIG. 2 is a flow diagram representing a vapor power plant system similar to that depicted in FIG. 1, however, illustrating the invention in connection with a vapor generator employing primary superheater, intermediate superheater and finishing superheater.

Referring now to the drawing in which like reference characters are used throughout to designate like elements, the diagrammatic representation of FIG. 1 shows a forced flow once-through vapor generator 10. A feed pump 12 is organized to supply working fluid to vapor generator 10 from a source such as tie-aerator 14 by way of condui-t 16 and via a fluid preheater 18. To control or shutoff the flow of a working fluid a feed valve 20 is provided in conduit 16. The working 'fluid passes through econornizer 22, conduit 23, vapor generating section 24, conduit 25, primary superheater 26, conduit 27, finishing superheater 28 and conduit 29 to a point of use such as vapor turbine 30. A valve 31 is provided in conduit 29 to shut-01f the flow of working fluid to turbine 34). After having given up a major portion of its thermal energy, the vapor is condensed in condenser 32 and the condensate returned to de-aerator 1 3 through conduit 33 via condenser pump 34 and heater 35.

Fuel and air for combustion are supplied to vapor generator 1% by way of burner 36 in any conventional manner. The hot combustion gases produced by the burning of the fuel pass in heat exchange relation over the heat absorbing surfaces of the vapor generating section 24, superheating sections 26 and 28 and economizer 22. Other conventional means of supplying heat to the vapor generator may be used in connection with the invention.

In accordance with the invention a source 38 of auxiliary vapor is provided for supplying vapor during the start-up operation to de-aerator '14 by way of conduit 40 including valve 41, and to primary superheater 26 by way of conduit 42 including valve 43. An important elemen-t of the inventive combination herein disclosed is the provision of a recirculating conduit 44 including valves 46 and recirculating pump 48 for the recirculation of working fluid from the outlet of vapor generating section 24- to the inlet thereof. In additon an overflow conduit 50 is provided including valve 51, which connects the outlet of vapor generating section 24 to a point of low pressure such as the hot well of condenser 32. Furthermore the invention contemplates the use of a by-pass conduit 52 including valve 53 for by-passing the turbine during an early phase of the start-up operation. Another important element of the inventive combination is the provision in conduit 25 of a shut-off valve 54 including a throttling valve 56 arranged in conduit 57 which bypasses valve 54. The purpose of bypass valve 56 is to obtain throttling with high pressure drop and/or small flow quantities, while the main shut-0E valve 54 is designed for relatively low pressure drops and large flow quantities.

The forced flow modified once-through vapor generator is started up according to the invention with the following general considerations in mind.

First, as earlier mentioned herein, the vapor generating power plant is divided into two main portions. These are separated by a so-called boiler shutolf and throttling valve 54, 56. With this valve closed it is possible by use of vapor obtained from an auxiliary source 38 and superheated by passing it through superheaters 26 and 28, to warm up and roll the turbine long before any vapor has been generated in the vapor generating portion 24 of the generator 10. During the time the turbine is thus being prepared for full operation with auxiliary vapor, the vapor generator is also being brought up to temperature and pressure with a vaporizable fluid which fluid bad previously been de-aerated also by the use of vapor obtained from auxiliary source 38.

Accordingly, the starting up operation of the forced flow once-through vapor power plant commences with the closing of the boiler shutoff valve 54 and bypass and throttling valve 56, and the opening of boiler extraction 3 or overflow valve 51. Opening of valve 41 permits vapor to flow from the auxiliary vapor source 38 to the deaerator 14. Vaporizable fluid is pumped from the deaerator through economizer 22 and vapor generating section 24 by means of feed pump 12 via feed valve 20. This fluid is first being discharged to a point of lower pressure such as condenser 32 by way of extraction or overflow line 50 and extraction valve 51, while the unit is being fired up. The heated fluid is thus discharged through extraction valve 51 until the so-called clean-up operation of the vapor generator is completed, i.e.', until the working fluid has been purged of decontaminants and oxygen which may have been present in the working fluid. At this time feeding of the working fluid is discontinued by closing feed valve 20 and also by closing extraction valve 51, with the latter however being set to open automatically at a predetermined higher pressure. This is necessary in order to allow for overflow due to expansion of the fluid as the fluid is being heated in the vapor generating section 24. I

A second consideration of the present invention is the provision for protecting the tube lined walls 24 of the furnace from overheating while the feed valve 23 is closed. This is accomplished by recirculating the working fluid from the outlet of the vapor generating section to the inlet thereof by Way of conduit 44 and valve 46 and by means of recirculating pump 48. Recirculation of the working fluid thus serves two purposes. First, it provides for eflicient cooling of the tubular furnace surface exposed to radiant heat, thereby permitting a faster increase of the firing rate. And second, such recirculation simultaneously results in a quicker heating of the fluid since none of the heated fluid is being discharged to waste. Such discharge and waste of heat would be unavoidable without recirculation since a minimum velocity of the working fluid must be maintained in the furnace tubes to prevent overheating thereof.

While the vapor generating portion of the unit is thus prepared for full operation in a minimum of time by virtue of the recirculation circuit and the use of auxiliary vapor, the turbine is warmed up at the same time and rolled also by being supplied with auxiliary vapor from source 38 with this vapor having been superheated in superheaters 26 and 28. The auxiliary vapor thus performs three important functions. First, it permits the warming up and rolling of the turbine long before the vapor generating section 24 can supply the vapor for this operation. Second, the auxiliary vapor serves as a cooling medium for cooling the heating surfaces of superheaters 26 and 23 which are exposed to the hot combustion gases that are being produced for the purpose of heating the working fluid, in vapor generating section 24. And, third, 7

the auxiliary vapor provides the heat required for speedy de-aeration of the working fluid, thus contributing to a quick cleaning up of the fluid at start up of the vapor generator.

When the fluid contained in vapor generating section 24 and continually being recirculated thereabout has reached a temperature and pressure exceeding the temperature' and pressure in the superheater 26 by a predetermined desired amount, valve 56 in bypass 57 is opened with the high temperature fluid expanding into primary superheater 26. The difference in pressure and temperature between the fluid or vapor in vapor generating section 24 and that in superheater 26 is chosen to be of such an amount that the throttling action taking place in valve 56 desirably results in a flashing of vapor Without any appreciable amount of liquid entering the primary superheater 26. Simultaneously with the opening of bypass valve 56 feed valve 20 is gradually being opened to reestablish flow of working fluid into the vapor generator. Also the flow of auxiliary vapor is proportionally reduced by controlling valve 43. The feeding of relatively cool working fluid into economizer 22 and vapor generating section 24 requires a corresponding increase in heat input tothe vapor generator 10. Flow of high pressure, high temperature fluid from vapor generating section 24 to primary superheater 26 continues through valve 56 until the pressure in primary superheater 26 approaches that prevailing in vapor generating section 24. At this time valve 54 is opened and valve 43 closed to establish normal operation of the vapor generator and associated turbine.

FIG. 2 shows a representation of a forced flow vapor generating system similar to that illustrated in FIG. 1, but with the invention applied to a power plant having primary superheater 26, intermediate superheater 58 and finishing superheater 28. In the embodiment of FIG. 2 the shut-cit valve 54 of FIG. 1 is now designated 54a and is located in the conduit 59 leading from the primary superheater 26 to the intermediate superheater 58. This is in contrast to FIG. 1 wherein the. shut-oil valve 54 is located between vapor generating section 24 and primary superheater 26. In addition, the auxiliary vapor conduit 42 of FIG. 1 is now designated 42a and is connected to the inlet or" intermediate superheater 58. Also the over flow conduit 50 of FIG. 1, now designated 50a in FIG. 2 is connected to the outlet of the primary superheater 26. As in FIG. 1 a conduit 57a with valve 56a is provided in FIG. 2 for bypassing valve 54a also suitable valves 43a and 51a are installed in conduits 42a and 58a respectively.

The start-up operation and sequence of the power plant shown in FIG. 2 is substantially the'same as that earlier herein described in connection with the arrangement shown in FIG. 1. The main reason for locating valve 54a after the primary superheater 24 is that a higher temperature of the working fluid can thereby be obtained prior to throttling the fluid by passing it through valve 56a. Such higher temperature which is most cases should be in the neighborhood of 800 F., gives assurance that only dry vapor enters the superheater surface 58.

While specific embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein Without departing from the spirit and scope of the invention as set forth in the appended claims.

What I claim is:

1. In a forced flow modified once-through type steam power plant having a steam generating section, a steam superheating section and a steam turbine serially connected in the order named, means for supplying feedwater to said steam generating section, means de-aerating the feedwater, means for starting up said steam boiler and said turbine with only steam flowing through said steam superheating section comprising a cutoff valve arranged cutofl' valve is closed, a conduit connecting said super- 7 heating section to said auxiliary steam source and arranged to convey steam from said auxiliary steam source to said superheating section and to said turbine when said cutofl valve is closed, a recirculating conduit connecting a point downstream of said steam generating section with respect to water flow with a point upstream thereof, and means for recirculating water through said recirculating conduit around said steam generating section when said cutofi valve is closed.

2. In a forced flow modified once-through type steam power plant having a steam generating section, a steam superheating section and a steam turbine serially connected in the order named, means for supplying feedwater to said steam generating section, means for de-aerating the feedwater, means for starting up said steam boiler and said turbine with only steam flowing'through said steam superheating section comprising a cutoff valve arranged to control fluid flow between said steam generating and steam superheating sections, a source of auxiliary steam, a conduit connecting said auxiliary steam source with said de-aerating means and arranged to convey steam from said steam source to said de-aerating means when said cutoff valve is closed, a conduit connecting said superheating section to said auxiliary steam source and arranged to convey steam from said auxiliary steam source to said superheating section and to said turbine when said cutoff valve is closed, a recirculating conduit connecting a point downstream of said steam generating section with respect to water flow with a point upstream therof, means for recirculating water through said recirculating conduit around said steam generating section when said cutoff valve is closed, and a valve controlled relief conduit connecting said steam generating section to a point of lower pressure for maintaining a desired pressure in said steam generating section.

3. In a forced flow modified once-through type steam power plant having a steam generating section, a steam superheating section and a steam turbine serially connected in the order named, means for supplying feedwater to said steam generating section, means for de-aerating the feedwater, means for starting up said steam boiler and said turbine with only steam flowing through said steam superheating section comprising a cutoff valve arranged to control fluid flow between said steam generating and steam superheating secitons, a source of auxiliary steam, a conduit connecting said auxiliary steam source with said de-aerating means and arranged to convey steam from said steam source to said de-aerating means when said cutoff valve is closed, a conduit connecting said superheating section to said auxiliary steam source and arranged to convey steam from said auxiliary steam source to said superheating section and to said turbine when said cutoff valve is closed, a recirculating conduit connecting a point downstream of said steam generating section with respect to water flow with a point upstream thereof, means for recirculating water through said recirculating conduit around said steam generating section when said cutoff valve is closed, a valve controlled relief conduit connecting said steam generating section to a point of lower pressure and for maintaining a desired pressure in said steam generating section, and a valve controlled relief conduit connecting said steam superheating section to a point of lower pressure for controlling the pressure in said steam superheating section.

4. In a forced flow once-through type steam power plant having a steam generating section, a first steam superheating section, a second steam superheating section and a steam turbine serially connected in the order named, means for supplying feedwater to said steam generating ection, means for de-aerating the feedwater, means for starting up said steam boiler and said turbine with only steam flowin through said second steam superheating section comprising a cutoff valve arranged to control fluid flow between said first steam superheating and said second steam superheating sections, a source of auxiliary steam, a conduit connecting said auxiliary steam source with said de-aerating means and arranged to convey steam from said steam source to said d e-aerating means when said cutoff valve is closed, a conduit connecting said second superheating section to said auxiliary steam source and arranged to convey steam from said auxiliary steam source to said second superheating section and to said turbine when said cutoff valve is closed, a recirculating conduit connecting a point downstream of said steam generating section with respect to Water flow with a point upstream thereof, and means for recirculating water through said recirculating conduit around said steam generating section when said cutoff valve is closed.

5. Apparatus as defined in claim 4 wherein a valve controlled relief conduit is provided connecting said first steam superheating section to a point of lower pressure for controlling the pressure in said first steam superheating section,

6. Apparatus as defined in claim 5 wherein a valve controlled relief conduit is provided connecting said second steam superheating section to a point of lower pressure for controlling the pressure in said second steam su perheating section.

7. A method of starting up a forced flow modified once-through type vapor generator and associated turbine by use of vapor from an auxiliary vapor source, said generator having a de-aerator and first heating surfaces including vapor generating surface and second heating surfaces including a superheater serially connected therein, a vaporizable fluid flowing through said first and second heating surfaces wherein it is vaporized and superheated by the passage of heat containing gases thereover so that only vapor flows through said second heating surfaces, a vapor driven turbine receiving vapor from said second heating surfaces, the invention comprising starting up with supplying vapor from said auxiliary vapor source to said de-aerator to de-aerate said vaporizable fluid, flowing said vaporizable fluid through only said first heating surfaces to urge said first heating surfaces of contaminants, and then discontinuing feeding of said vaporizable fluid to said first heating surfaces and recirculating said fluid around said first heating surfaces without condensing it and maintaining substantially the same pressure throughout, supplying vapor from said auxiliary source to said second heating surfaces only, while commencing the passage of heating gases over said first and second heating surfaces, heating said vaporizable fluid that is recirculating through said first heating surfaces to produce vapor at a selected temperature and pressure, heating said auxiliarly supplied vapor in said second heating surfaces to a selected temperature and pressure, roll and synchronize said turbine with said auxiliarly supplied vapor, gradually increasing the heat content of said heating gases flowing over said first and second heating surfaces to achieve a temperature of the vapor leaving said first heating surfaces such that the steam in said second heating surfaces remains in an essentially dry state, gradually passing a portion of said vapor from said first heating surfaces to said second heating surfaces while admitting a corresponding portion of vaporizable fluid to said first heating surfaces and proportionally decreasing the flow of vapor from said auxiliary source to said second heating surfaces, progressively increasing the flow of vaporizable fluid to said first heating surfaces in direct relation to the said increase in heating gas flow to maintain only vapor flowing to said second heating surfaces, and discontinuing flow of vapor from said auxiliary vapor source to said second heating surfaces.

8. A method of starting up a forced flow modified oncethrough type vapor generator and associated turbine by use of vapor from an auxiliary vapor source, said generator having a de-aerator and first heating surfaces including vapor generating surface and second heating surfaces including vapor heating surface serially connected therein, a vaporizable fluid flowing through said first and second heating surfaces wherein it is vaporized and superheated by the passage of heating gases thereover so that only vapor flows through said second heating surfaces, and a vapor driven turbine receiving vapor from said second heating surfaces, the invention comprising the steps of:

(1) shutting off flow between said first and second heating surfaces;

(2) heating vaporizable fluid in said first heating surfaces by supplying heat from said heating gases to the heating surfaces thereof with said vaporizable fluid having first been de-aerated by using heated vapor from said auxiliary vapor source;

(3) discontinuing flow of said vaporizable fluid to said first heating surfaces and recirculating said vaporizable fluid around said heating surfaces while maintaining the pressure thereof substantially equal throughout;

(4) simultaneously with steps 2 and 3 supplying vapor to said second heating surfaces from said auxiliary vapor source;

(5) heating the vaporizable fluid in said first heating surfaces by the passage of said heating gases thereover to gradually raise the temperature and pressure thereof to desired values;

(6) simultaneously with step 5 heating the vapor in said second heating surfaces by the passage of said heating gases thereover, to a desired temperature and pressure While rolling and synchronizing said turbine;

(7) controlling the temperature and pressure of the vapor produced in said first heating surfaces such that the vapor in said second heating surfaces remains in an essentially dry state;

(8) gradually establishing flow of vapor from said first to said second heating surfaces With a proportional increase of Vaporizabie fluid flow to said first heating surfaces and a gradual decrease and tidal discontinuance of the flow of the vapor from said auxiliary vapor source to said second heating surfaces.

9. A method of starting up a forced flow modified oncethrough type vapor generator and associated turbine by use of vapor from an auxiliary vapor source, said generator having first heating surfaces including vapor generating surface and second heating surfaces including vapor heating surface serially connected therein, a vaporizable fluidflowing through said first and second heating surfaces wherein it is vaporized and superheated by the passage of heating gases thereover so that only vapor flows through said second heating surfaces, and a vapor driven turbine receiving vapor from said second heating surfaces, the invention comprising the steps of:

(1) shutting ofi flow between said first and second heating surfaces;

(2) heating vaporizable fluid in' said first heating surfaces by supplying heat from said heating gases to the heating surfaces thereof;

(3) discontinuing flow of said vaporizable fluid to said first heating surfaces and recirculating said vaporizable fluid around said heating surfaces while maintaining the pressure thereof substantially equal throughout;

(4) simultaneously with steps 2 and 3 supplying vapor to said second heating surfaces from said auxiliary vapor source; a

(5) heating the vap'orizable fluid in, said first heating surfaces by the passage of said heating gases thereover to gradually raise the tempe'rature and pressure thereof toade'sire'd values; p 7 a (6) simultaneously with step 5 heating the vapor in said second heating surfaces by the passage of said heating gases thereover, to a desired temperature and pressure While rolling and synchronizing said turbine;

(7) controlling the temperature and pressure of the discontinuance of the flow of the vapor from said auxiliary vapor source to said second heating surfaces.

References (Iited by the Examiner UNITED STATES PATENTS 2,116,587 5/1938 Toensfeldt -105 2,184,224 12/1939 Lucke 60-102 2,989,038 ,6/1961 SchWarz 122-406 3,019,774 2/1962 Beyel'lein 122-406 SAMUEL LEVINE, Primary Examiner. ROBERT R. BUNEVICHExaniiner. 

1. IN A FORCED FLOW MODIFIED ONCE-THROUGH TYPE STEAM POWER PLANT HAVING A STEAM GENERATING SECTION, A STEAM SUPERHEATING SECTION AND A STEAM TURBINE SERIALLY CONNECTED IN THE ORDER NAMED, MEANS FOR SUPPLYING FEEDWATER TO SAID STEAM GENERATING SECTION, MEANS DE-AERATING THE FEEDWATER, MEANS FOR STARTING UP SAID STEAM BOILER AND SAID TURBINE WITH ONLY STEAM FLOWING THROUGH SAID STEAM SUPERHEATING SECTION COMPRISING A CUTOFF VALVE ARRANGED TO CONTROL FLUID FLOW BETWEEN SAID STEAM GENERATING AND STEAM SUPERHEATING SECTIONS, A SOURCE OF AUXILIARY STEAM, A CONDUIT CONNECTING SAID AUXILIARY STEAM SOURCE WITH SAID DE-AERATING MEANS AND ARRANGED TO CONVEY STEAM FROM SAID STEAM SOURCE TO SAID DE-AERATING MEANS WHEN SAID CUTOFF VALVE IS CLOSED, A CONDUIT CONNECTING SAID SUPERHEATING SECTION TO SAID AUXILIARY STEAM SOURCE AND ARRANGED TO CONVEY STEAM FROM SAID AUXILIARY STEAM SOURCE TO SAID SUPERHEATING SECTION AND TO SAID TURBINE WHEN SAID CUTOFF VALVE IS CLOSED, A RECIRCULATING CONDUIT CONNECTING A POINT DOWNSTREAM OF SAID STEAM GENERATING SECTION WITH RESPECT TO WATER FLOW WITH A POINT UPSTREAM THEREOF, AND MEANS FOR RECIRCULATING WATER THROUGH SAID RECIRCULATING CONDUIT AROUND SAID STEAM GENERATING SECTION WHEN SAID CUTOFF VALVE IS CLOSED. 